I had some trouble with home assembly of some PCBAs. I've got an STM32F411xC (datasheet here).
Anyway, After reworking it a bit, and some issues elsewhere on the board were uncovered (all related to oversights with soldering technique), the first board was toast...Missing pads and so on..
So, I moved to the next clean board, and started fresh...One component at a time, and testing along the way for continuity, resistance, etc.
The first and most technically troublesome part to put down was the STM32F4 in a 64 pin LQFP, so I dropped that thing down and took a reading across the 3.3V rail and GND, and everything looked good...wide open.
So, imagine this...I only have the STM32F4 on the board, that's it...I put 3.3V on the board from an external supply, and it shorts out, 350mA before the current control kicks in. Now, I've got 26kohm between 3.3V and GND after removing power...
So, after a day of double checking pinout, orientation of the chip (found here), the thing I tried was pulling up the VCAP1 pin and leaving it floating...So, I read a little about it and see that VCAP1 is pretty serious when it says to hang 2x2.2uF or 4.7uF off of it, so I do that...
I get a new IC, desolder the old one, put it down, measure resistance between power and ground, make sure all the pins are really connected to the board well, ring out all the VDD's and VSS's AND slap down two 2.2uF caps on VCAP1.
I turn it on, and still, short circuit.
What the heck is going on here? This circuit is so simple, it's two components...The STM32F411 and a pair or 2.2uF caps...
I'm tellin' ya...You hook this circuit up, it'll short right out and get real hot, real quick. What is the GOTCHA here that I'm missing?